I think this refers to a love triangle. Wikipedia: A love triangle is a romantic relationship involving three people. While it can refer to two people independently romantically linked with a third, it usually implies that each of the three people has some kind of relationship to the other two.
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Wikipedia:
A love triangle is a romantic relationship involving three people. While it can refer to two people independently romantically linked with a third, it usually implies that each of the three people has some kind of relationship to the other two. The term "love triangle" almost always implies that the arrangement is unsuitabl